An apparatus for operating by means of compressed air and arranged for expulsion of fixing elements fed forward out from a magazine is previously known, in which apparatus there is arranged, in a cylinder housing, a movable cylinder in which there is arranged, in turn, a piston which is displaceable between two end positions. The apparatus comprises, for controlling the air flow for displacement of the cylinder and the piston, a number of valve bodies for delivery as well as evacuation of compressed air to the cylinder housing.